Response characteristics of Herbst corpuscles in the interosseous region of the pigeon's hind limb

The Herbst corpuscle, found only in birds, is one of the morphologically distinct types of lamellated sensory nerve endings. Its response properties were studied electrophysiologically in anesthetized pigeons by recording from: (A) afferents emerging from single Herbst corpuscles located in the interosseous region of the shank, (B) from vibration-sensitive cells found in the dorsal root ganglia near the lumbosacral enlargement of the spinal cord, and (C) from nerve fibers dissected out of the sciatic nerve. Vibration-sensitive cells in the dorsal root ganglia and in sciatic nerve fibers exhibited properties that were very similar to those found at the Herbst corpuscle itself. All three recording approaches indicated that Herbst corpuscles are vibration-sensitive mechano-receptors with broad bandpass tuning curves. With all approaches, the lowest threshold always fell in the frequency range between 400 and 800 Hz. The value of the threshold, however, varied with the method, being as low as 0.08 m with method C and as high as 1 m with method A. Regardless of method, these neurons exhibited no spontaneous activity, and their firing displayed a special sensory coding pattern at high stimulus amplitude: the nerve impulses were phase locked to the stimulus cycle, exhibiting a 1:1 relationship with it up to a frequency of 500 Hz. Comparison of these data with prior behavioral data suggests that the Herbst corpuscle peripheral mechanoreceptors are part of a vibratory sensory system which acts as a warning device, given attentive behavior.Abbreviations AP action potential - INTH interspike interval histogram